it's the act of clowning on a friend by pretending to give him dabs, or pound, or any handshake, then suddenly takes it away & makes a sharks fin on the forehead. trust me, it is a lot funnier went you are drunk.

as i was leaving work, i was shaking hands with co-workers and then i saw this guy who just messes with me a lot. i put my hand out to shake his hand, i pulled back & said " you got sharked!" everybody just started laughing so much, but only a few people get the joke.